CONSTITUTION: Accumulated glass fibers 2 are fed into a space between the receiving plate 6 and the press plate 7 of a needling device, and a lifting plate 5 is lowered. Needles 8 are penetrated into the glass fibers 2 and subsequently the lifting plate 5 is lifted to pull out the needles 8 from the glass fibers 2. The glass fibers 2 caught by the hooks of the needles 8 are pulled down in loop states to interlace with other fibers for the production of a fiber mat.